Biological Classification

Scientists have organized the vast array of biological life into a hierarchical system known as the Biological Classification or Scientific Classification.  It is a method of grouping all life into similar groups based upon physical and biological characteristics.  The modern ability to use DNA for classification purposes has begun to modify and refine these relationships.  In fact, there is now a new category, a Domain, that supersedes the Kingdom.  There are three domains:  Bacteria, Archaea (single-celled life forms), and Eukarya (multi-celled, complex life forms such plants, fungi, and animals). 

Things aren't always as simple as they seem and this is no exception.  Within this neat and tidy hierarchy are a legion of sub-orders, sub-families, supra-orders, infra-orders, tribes, etc., etc., etc. It just makes your head spin! But it also demonstrates how Life on Earth has developed into a myriad and complex relationship and how stupendously varied and wonderful it can be.

How do scientists determine how a particular animal should be classified?  They examine the physical and biological characteristics of the organism and group it with others of similar traits.  It is thought that we have so far classified only a small fraction of all life on earth. 

Within each category (kingdom, order, etc.) there are many members, and as you can imagine, the lower down you go in the classification, the more the members muliply.  In other words, there are more species on earth than there are families.

Throughout this website you will see information on both the biological classification as well as a phylogenetic classification.  The latter simply traces the relationship between animals based on evolutionary characteristics:  for example, pterosaurs share a common ancestor with dinosaurs even though they are a separate evolutionary branch.  You can see an example of phylogenetic diagram (called a cladogram) in the Pterosaur Introduction page. 

I have included a table providing examples of the classification of common animals.  It is hoped that this will help you become more comfortable with the classification tree.

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